create
Create a hashed map bin at the given level and with the given bit vector. The number of 1 bits in the bit vector determine how many sub-bins to allocate. Start each sub-bin as an empty linear bin, with the expectation that it will be populated during subsequent initialization of this bin.
Return
A hash map bin suitable for adding entries to. The bin is denormalized, with all sub-bins set to empty linear bins.
Parameters
my
The hash tree depth, which controls how much to shift hashes.
bit
The Long containing a 1 bit for each sub-bin slot.